Abstract
A series of direct observation of complete miscibility between H2O fluids and island arc andesite/rhyolite magmas has been conducted using Bassett's type externally heated diamond anvil cell. The supercritical behaviors are observed between H2O fluids and Fuji 1707 magmas with chemical compositions from andesite (62 weight % SiO2) to rhyolite (69 % SiO2). Such a supercritical behavior between H2O fluids and magmas equilibrated with mantle peridotite system remains uncertain. This study is the first observation of a supercritical behavior of natural andesite and rhyolite with H2O fluids, suggesting a possibility of a second critical point between magmas and aqueous fluids in the depths of the Earth.
